The invention relates to an apparatus for manufacturing products from an at least thermoplastically deformable material. Such a method is known, for instance, as injection molding.
With known injection molding techniques, as a rule, the material to be formed such as plastic is heated in a plasticizing device to a temperature such that the material becomes virtually liquid, at least plastic and low-viscous, whereupon the material is introduced under high pressure into a mold cavity of an injection molding mold. In this mold cavity, the material is distributed such that the mold cavity is completely filled, whereupon the material is allowed to cure by cooling down. Thereupon, the product is taken out by opening the mold and ejecting the product.
For such known injection molding techniques, a particularly high feed pressure is to be used, especially when thin-walled products are formed, in particular if the flow paths in the mold cavity closely approach the melt flow index (MFI) of the materials to be used. Therefore, the same holds in particular when the flow paths in the mold cavity are relatively long. It is clear that with plastics with a high viscosity and/or a low melt flow, these problems occur to a larger extent. As a result, limitations are imposed on the minimum and maximum sizes of products, in particular on lengths of flow paths, on passage widths of such flow paths, on the duration of the injection molding cycles, on the materials to be used and on the minimum wall thicknesses of products, in particular of large, flat parts.
The use of compression molding is already known. Here, into a mold cavity of a partly open mold, an amount of plastic is introduced, required for 25 forming a desired product in this mold cavity. After the plastic has been introduced into the mold cavity, the mold is closed further, so that the plastic is pushed away for filling the further mold cavity. Therefore, with such an apparatus, at the start of the introduction of the plastic, the mold parts are to be held partly away from each other, and only afterwards to be brought onto each other relatively slowly but with high pressure. The danger exists that then, the plastic is not uniformly distributed, so that, for instance, a part of the material can be pressed sideways from the mold cavity before the mold cavity is completely closed. Also, the danger exists that insufficient or, conversely, too much plastic is introduced into the mold cavity. In this latter case, skin formation will occur between the mold halves and, moreover, it will not be possible to close the mold completely. This leads to irregularly formed products and, moreover, to pollution of the mold. A further disadvantage of this apparatus is that when materials are used with a low viscosity and/or with shallow mold halves, the material flows from the mold cavity before the mold halves are moved together, so that the earlier mentioned problems occur to an even larger extent.